During the power on operation of a virtual machine (VM) on a host, the host file system creates a swap file. The swap file is a file in storage used by the virtualization layer of the host to swap the VM's memory in and out of the host's physical memory. As a result of the usage of swap files, the host makes a larger portion of memory available to individual VMs than would be possible if the physical memory resources were strictly divided among all VMs on the host. Typically, the file system creates the swap file as a thick file with a size equivalent to the memory configured for the VM. As a result, the file system fully allocates the storage space needed for the swap file at the time of creation. With large VM memory configurations (e.g., up to 2 TB), the time taken to create a swap file may be nontrivial, and can slow down the overall power on operation significantly.